Azaboranes



United States Patent 3,428,439 AZABORANES Walter R. Hertler, Kennett Square, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. ontinuation-in-part of applications Ser No.

490,661 andfSer. No. 490,712, Sept. 27, 1965. This application Nov. 18, 1966, Ser. No. 595,357

US. Cl. 23-358 8 Claims Int. Cl. C01b 21/06 ABSTRACT OF THE DISCLOSURE Azaboranes of the formula MHNB H or RR'R"NNB H where M is a cation and the Rs are selected hydrocarbyl groups. The azaboranes are prepared by reacting an N- thionitrosodialkylamine with decaborane at -25 C. to 100 C. in an inert solvent. The azaboranes are useful as blowing agents, in electrical resistors and as reducing agents.

MHNBgH g and (2) RR'R"NNB H In Formula 1, the nucleus nitrogen is additionally bonded to the hydrogen, while in Formula 2, it is additionally bonded to the nitrogen of the NRR" group. The com; pounds of Formula 2 are N-(substituted-amino) derivatives of the compounds of Formula 1. R and R" are defined as alkyl groups of up to 12 carbon atoms each or together are alkylene of 2-12 carbon atoms. M and R represent one equivalent of a cation selected from alkali metals, alkaline earth metals, GG 'N+, G P+, G S G.,As+ or G Sb+. In addition, R can be a straight chain alkyl group of 1-3 carbon atoms or an aralkyl group of 7-10 carbon atoms, and in these two instances, the compounds of Formula 2 can be considered to be an innersalt or zwitterion.

G is defined as a monovalent hydrocarbyl group of up to 18 carbon atoms that is free of aliphatic carbon-tocarbon unsaturation, and G is a monovalent hydrocarbyl group of up to 18 carbon atoms that is free of aliphatic carbon-to-carbon unsaturation and is bonded to N through an aliphatic carbon atom. Preferably, G and G each contain up to 12 carbons. Any two G or G groups in the same cation can also be joined (bonded) directly to each other or through an oxygen hetero atom, to form a divalent alkylene group or oxygen-interrupted (mono-oxa) alkylene group of 4-8 carbons. The term free of aliphatic carbon-to-carbon unsaturation means that the hydrocarbyl group contains no aliphatic ethylenic or acetylenic bonds, i.e., the only unsaturation that may be present is aromatic.

Examples of these cations include benzyltrimethylammonium, N,N-diethyl-2,5-dimethylpyrrolidinium, dodecyltrimethylammonium, cyclohexyltrimethylammoniurn, N- methyl N octadecylmorpholinium, tetrabenzylphosphonium, ethylpentamethylene-p-tolylphosphonium, benzylhexadecyldimethylphosphonium, isobutylethylmethylisopropylphosphonium, benzyltris(4 biphenylyDphosphonium, triphenylsulfonium, methyltetramethylenesulfonium, methyldipentylsulfoniurn, cyclohexyldimethylsulfonium, tetramethylarsonium, 2-biphenylyltrimethylarsonium, methyltri(p-tolyl)arsonium, tetraphenylstibonium, decyltriphenylstibonium, t-butylethyldimethylammonium, and the like.

Of the G- and G-substituted cations above, the ammonium, phosphonium, and sulfonium are preferred because of availability. For the same reason, those containing only lower alkyl substituents (1-8 carbon atoms) are preferred.

The group G can only be bonded to the nitrogen through an aliphatic carbon atom, i.e., G cannot be aryl where the aryl group is bonded directly to the nitrogen.

Examples of alkyl and aralkyl R groups include 3, z 5 3 v 6 5 z P- 3 e 4 z p-(CH CHC H,CH and the like.

The NB H nucleus of the compounds of this invention is believed to be, at least in part, a polyhedral fragment consisting of nine boron atoms: and one-nitrogen atom, with three hydrogen atoms in bridging positions or EH groups, but the exact geometrical configuration is not known at this time.

The compounds of Formula 2 where R is M can be prepared from an N-thionitrosodialkylamine and decaborane( 14) according to the equation where R and R" are alkyl groups of up to 12 carbons each or together are an alkylene group of 2-12 carbons.

The reaction is carried out at temperatures ranging from 25 to 0, preferably 0-25 C., in an inert solvent. Neither pressure nor time of reaction is critical. Atmospheric pressure is preferred for convenience, although subatmospheric or superatmospheric pressures may be employed. The solvent employed is preferably an ether, and most preferably a dialkyl ether of 2 to 10 carbons or a cyclic aliphatic hydro carbon ether, such as dioxane, tetrahydrofuran, and the like. Aromatic hydrocarbon solvents, such as benzene or xylene, or ester solvents such as ethyl acetate can also be employed.

The ratio of reactants is not critical and can range from 1:10 or more to 10:1 or more, although preferably the ratio is usually about 2:1 RR"NNS to B H Also produced in the reaction is the anion B H S-. Both anions are contained in a solid mixture which forms during the reaction. Upon treating the solid with aqueous alkali-metal hydroxide (1-50 percent), e.g., NaOH, the alkali-metal salt of each anion is obtained in the aqueous layer. The aqueous solution is then treated With a solution of a compound containing a precipitating cation, e.g., tetramethylammonium chloride, whereupon the tetramethylammonium salts containing both anions precipitate. The compounds containing the two different anions can be separated by taking advantage of their different solubilities in certain solvents. For example, upon treatment with hot ethanol, the (CH NB H S is precipitated While the (CH NRR"NNB H dissolves. Upon removing the solvent, the tetramethylammonium salt of the compound of Formula 2 is isolated. Alternatively, the mixture of salts can be dissolved in a solvent such as acetonitrile and the salts selectively precipitated by careful addition of a relatively poor solvent, such as ether, benzene or chloroform.

Once the tetramethylammonium salt is obtained, any of the other cations defined by M or R can replace the tetramethylammonium cation by well-known cation exchange procedures. Specific cation-exchangeres'ins'can be employed.

Once the salts, M(R'R"N NB H are obtained, the cation can be replaced by alkyl or aralkyl groups (to complete the definition of R in Formula 2) through alkylation of the salts with an alkylating agent 'R X wherein R is straight chain alkyl of 13 carbon atoms or aralkyl of 710 carbon atoms, and X is a leaving group of valence g. The term leaving group is used as described in Gould, Mechanism and Structure in Organic Chemistry, Holt Dryden, 1959, p. 261. Preferably, X is chloride, bromide, iodide, sulfate, or a C -C hydrocarbonsulfonate free of aliphatic unsaturation, i.e., any unsaturation present is aromatic. Thus, examples of R X include dimethyl sulfate, methyl iodide, benzyl chloride, methyl p-toluenesulfonate, ethyl methanesulfonate, and the like. This alkylation process is generally carried out at mole ratios of 'R X to tRR"NNB H of at least 1:1 and can be as high as 200:1. Temperatures will be between 25 and 100 C., but preferably will be between 25-35 C. Neither pressure nor time is critical. Atmospheric pressure is usually employed for convenience, while the time can range from a few seconds to 1 or more days. A convenient time of reaction at 35 C. is about one hour.

The alkylation is carried out in an inert solvent. Suitable solvents include aliphatic or aromatic hydrocarbon ethers such as 1,2-dimethoxyethane, di(2-methoxyethyl)ether, diphenyl ether, tetrahydrofuran, dioxane and the like; aliphatic or aromatic nitriles such as propionitrile, benzonitrile, and the like; esters such as propyl acetate, methyl benzoate, butyl propionate and the like; aliphatic alcohols such as cyclohexanol, butanol and the like; or ketones, as for example, acetone or acetophenone. Thus it is seen that the particular solvent employed is important only in facilitating isolation of the products.

Compounds of Formula 1 are obtained by treating a compound of Formula 2 with a reducing agent in a neutral or alkaline medium. lReducing agents employed include sodium, lithium, potassium or calcium metals, basic zinc dust or any basic hydrosulfite solution, such as an alkali metal hydrosulfite. With metallic reducing agents that react rapidly with water, a non-aqueous medium is employed as for example, ethers, such as tetrahydrofuran 1,2-dimethoxyethane, or dioxane. With alkali metals and alkaline earth metals, the temperature is critical and must be between about 50 and 75 C.; otherwise temperature is not critical.

The products of the invention are generally colorless, crystalline solids that are stable to air and to water at normal-to-moderate temperatures. Salts containing the RR"NNB H anion usually melt above about 150 C., and salts containing the NHB H anion usually melt above about 250 C. The hydrocarbylated, zwitterionic compounds *RR R"NNB H are insoluble in water but soluble in polar organic solvents, e.g., alcohol, acetone, and acetonitrile.

The products and processes of this invention are illustrated in further detail in the following examples.

EXAMPDE I To a stirred solution of 18.5 g. of decaborane(14) in 450 ml. of ether was added dropwise over 30 minutes at room temperature 200 ml. of 0.7 M N-thionitrosodimethylamine solution in ether. The mixture was stirred for an additional 30 minutes after addition was complete. The supernatant liquid was decanted from the gum which had separated, and the gum was washed with ether. The gum was extracted with about .200 ml. of aqueous sodium hydroxide solution. The extract was filtered, and the filtrate was treated with excess tetramethylammonium chloride. The resulting precipitate was collected by filtration and then extracted with warm ethanol, and the mixture was filtered. The filtered ethanol extract was concentrated under reduced pressure, and then treated 'with' about twice its' volume of 1 ilbenzene-cyclohexane to give 4.9 g. of (CH N(CH NNB H which was collected by filtration. The product was purified by recrystallization from ethanol-cyclohexane (ca. 2- 1) followed by recrystallization from a small volume of ethanol to give crystals with M.P. 197-198 (bubbling).

Analysis.Calcd. for C H B N C, 29.9; H, 12.5; B, 40.3; N, 17.4. Found: C, 30.1; H, 12.1; B, 40 .4; N, 17.4.

The product shows ultraviolet absorption in acetonirile solution at 285 m (61510) with a shoulder at 225 m (e6100). The H nuclear magnetic resonance spectrum,

of the product in acetonitrile-d at 60 mc. shows three peaks at 7.17 ((CH N+, relative intensity 4), 7.86-r (NCH relative intensity .74), and 7.97-r (N--CH relative intensity 1.1) suggesting the presence of two isomers.

Platinum-catalyzed acid hydrolyses of a similar sample gave 1750.3 and 1753.1 cc. of hydrogen per gram of sample, consistent with the equation 4N CH3 ZNNBQHUQ 3)4 )2+'( a)2 2 +8B(OH) 19H which requires 1762 cc. of hydrogen per gram of a)4 a)2 9 1z The use of other vN-thionitroso secondary amines in place of N-thionitrosodimethylamine in Example I gives products of the invention containing other hydrocarbyl groups as values of R and R". For example, 'N-thionitrosodibutylamine gives (CH N(C H NNB H N- thionitrospyrrolidine gives (CH N(CH NNB H N- thionitrosodecamethylenimine gives 3)4 2)10 9 12 and N-thionitrosodidodecylamine gives a)4- 1z 25)a 9 12 If salts containing other precipitating cations are substituted for tetramethylammonium chloride in essentially the procedure of Example I, the corresponding salts containing these cations and the R 'R NNB H f anion can be obtained. For example, tetranaphthylphosphonium iodide gives (C1qH7)4'P(CH3)2NNB9H12, methyltetram'ethylenesulfonium bromide gives GHQ-CHI tetraphenylarsonium chloride produces 's 5)4 a)2 9 i2 and tetramethylstibonium chloride gives Alternatively, a solution of (CH N(CH NNB H can be passed through a column packed with a sodium cation-exchange resin, and the solution of thus obtained can be treated with the salts containing the precipitating cations mentioned in the preceding paragraph, whereupon the salts containing these cations and the (CH NNB H anion precipitate.

EXAMPLE II solid. The product was purified by recrystallization from' acetonitrile-ethanol to give colorless crystals, which decomposed quite suddenly at 176.5" with formation of copious amounts of gas.

Analysis.--Calcd. for C H B N C, 19.7; H, 11.6; B, 53.3; N, 15.4. Found: C, 18.6, 20.6; H, 11.4, 11.3; B, 53.3, 52.8; N, 16.8

The ultraviolet spectrum of the product in acetonitrile shows absorption at 223 mp (E7100). The H n.m.r. spectrum of the product in acetonitrile-d shows a single peak at 7.027 (-N(CH The infrared spectrum of the product shows absorption characteristics of the --N(CH group at 1481 cmr There is no absorption attributable to NH.

Platinum-catalyzed acid hydrolysis of the product gave 2350.3 cc. of hydrogen per gram of compound, consistent with the equation which requires 2330 cc. of hydrogen per gram of a)3 9 12- By substituting other hydrocarbylating agents for the methyl iodide of .Example II, other products of the invention can be obtained. For example, propyl p-toluenesulfonate gives C H (CH NNB H benzyl chloride gives C H ,CH (CH NNB H and 3-phenylpropyl bromide giVCS C6H5CH2cH2cH2(CH3)2NNBQH12- EXAMPLE III A mixture of 3 g. of (CH N(CH NNB H12, 100 ml. of anhydrous tetrahydrofuran, and about 10 ml. of a 50% dispersion of metallic sodium inmineral oil was stirred at reflux for 20 hours under a nitrogen atmosphere. The mixture was cooled and treated with ethanol to destroy unreacted sodium, and then evaporated to dryness under reduced pressure. The residue was treated with water and pentane, and the layers were separated. The aqueous layer was treated with tetramethylammonium chloride, and the resulting precipitate was collected by filtration to give 1.89 of colorless solid. Crystallization from ethanol gave .24 g. of (CH NNHB H as colorless plates, M.P. 300.

Analysis.Calcd. for C H B N C, 24.2; H, 12.7; B, 49.0; N, 14.1. Found: C, 24.5; H, 12.4; B, 50.1; N, 14.6, 13.5, 13.7.

Platinum-catalyzed acid hydrolyses of the product gave 2084 and 2106 cc. of H per gram of compound in accord with the equation which requires 2140 cc. of H per gram.

The infrared absorption spectrum of the product shows absorption at 3390 (N-H str.) and 25802350 cm." (complex, B-H str.). The absence of absorption attributable to NH deformation confirms the presence of an N-H group rather than an NH group.

The 60 me. n.m.r. spectrum of (CH NNHB H in acetonitrile-d shows two peaks at 77.11 [(CH N] and 77.91 (sl. broad, N-H) in the ratio 12:1 consistent with the proposed structure.

By substituting other ammonium, phosphonium, sulfonium or stibonium salts for the tetramethylammonium chloride, such cation-containing salts can be precipitated. Thus, the tetranaphthylphosphonium, methyltetramethylene-sulfonium, tetraphenylarsonium and tetramethylstibonium salts can be obtained as described in Example 1.

EXAMPLE IV A solution of 0.60 g. of (CH NNHB H in about 100 ml. of 1:1 aqueous acetonitrile was passed through a column packed with a sodium cation-exchange resin. The eflluent solution of NaNHBgH z was concentrated under reduced pressure to about 25 ml., and excess solid cesium sulfate was added. The solid that precipitated was collected by filtration, washed, and dried, to give 0.63 g. of CsNHB H Part of the product was further purified by recrystallization from ethyl alcohol/benzene/cyclohexane.

Analysis.-Calcd. for H B CSN: H, 5.09; N, 5.45. Found: H, 5.40; N, 5.37.

The ultraviolet absorption spectrum of an aqueous solution of the product had an absorption of 218 mi (68570).

The sodium-ion-exchange resin was made from a commercial, sulfonated styrene copolymer cationexchange resin (Rexyn 101 (H)) by passing aqueous sodium chloride through a column filled with the resin until the efiluent was no longer acidic and then. washing the resin free of chloride ion with water.

Cation-exchange resins containing other alkali metals or alkaline earth metals in place of sodium can be prepared in the same manner. Thus, other cations defined in Formulas 1 and 2 can be obtained such as LiHNBgHm,

e m g 9 12) 2, s 12) 2,

Li (R'R"NNB H Ca(R'R"NNB H and the like.

The R' NNS reactant can be prepared by reacting a 1, l-dialkylhydrazine, e.g., 1, l-dimethylhydrazine with powdered sulfur at temperatures of 0 to 50 C. in an inert medium such as ether. The R NNS can then be isolated by ordinary methods, e.g., distillation or recrystallization. This procedure is described in copending application Ser. No. 413,989, filed Dec. 8, 1964, in the name of W. J. Middleton, now US. 3,344,135, and assigned to the assignee of record herein.

The compounds of this invention can be employed as blowing agents in the production of polymeric foams. For example, a sample of Elvax 250 ethylene-vinyl acetate copolymer was softened by heating, and a small portion of (CH NNB H was blended in. The resulting sample was then heated at 210, and a foam was produced. Similar results were obtained with ethylene-carbon monoxide copolymer, tetra-fluoroethylene-isobutylene copolymer, and Nordel ethylene-propylene copolymer.

The compounds of the invention are also useful in the preparation of electrical resistors. A cotton string can be impregnated with a nearly saturated solution of a compound of the invention, in a volatile solvent such as acetonitrile. When the string is removed, dried and burned, a coherent ash is left which resembles the original string in size and shape. This ash is sufiiciently coherent to permit embedding in parafiin for use as an electrical resistor. Resistors of up to 4200 ohms/mm. have been prepared in this fashion.

The novel compounds can be employed as reducing agents in preparing printed electrical circuitry. A circuit can be traced on paper using a solution of acetonitrile and one of the compounds of this invention. After evaporating the solvent, the tracings can be sprayed with an aqueous solution of palladium chloride. After rinsing, a metallic tracing of reduced palladium is left.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound selected from the group consisting of MHNB9H12 and RR R NNBgHlz Wherfiin R and R" are selected from the class consisting of,

individually, alkyl of up to 12 carbon atoms, and taken together, alkylene of 2 to 12 canbon atoms;

M is one equivalent of a cation selected from the class consisting of alkali metal, alkaline earth metal, GG N+, G P+, 6 8+, G,As+ and G Sb+ wherein G is hydrocarbyl of up to 18 canbon atoms that is free of aliphatic canbon-to-carbon unsaturation G is hydrocarbyl of up to 18 carbon atoms that is free of aliphatic canbon-to-carbon unsaturation and is bonded 7 to N through aliphatic canbon, and G and G can be joined to form a divalent group of 48 carbon atoms selected from the class consisting of ailkylene and mono-oxaalkylene; and

R is selected from the class consisting of M, straightchain alkyl of 1-3 carbon atoms and aralkyl of 7-10 carbon atoms.

2. The compound of claim 1 having the formula MHNB H wherein M is defined as in claim 1.

3. The compound of claim 1 having the formula R R'R"NNB H wherein R, R and R" are defined as in claim 1.

4. The compound of claim 3 having the formula R(CH NNB H wherein R is defined as in claim 3.

5. The compound of claim 1 having the formula 3)4 a)z 9 1z 6. The compound of claim 1 having the formula 3)a 9 12- 7. The compound of claim 1 having the formula (CH NNHB H References Cited UNITED STATES PATENTS 9/1964 Knoth 260-6065 2/1965 Miller et al 260 -606 OSCAR R. VERTIZ, Primary Examiner.

H. S. MILLER, Assistant Examiner.

US Cl. X.R. 

